Brit D-cell torpedo in icepack-bottom probe

A British robot submarine has penetrated under the Western Antarctic ice shelves to a distance of 60km, plunging to depths greater than 1000m. The "Autosub", built by boffins in Southampton, was powered by tens of thousands of ordinary D-cell batteries during its forays beneath the ice.

Autosub comes from the UK's National Oceanography Centre (NOC), and has been operating from the US icebreaker Nathaniel B Palmer off the floating Pine Island Glacier in the Amundsen sea. Here's a NOC vid of the yellow, torpedo-esque machine being recovered aboard ship:

"Autosub is a completely autonomous robot: there are no connecting wires with the ship and no pilot," says the NOC's Steve McPhail. "It has to avoid collisions with the jagged ice overhead and the unknown seabed below, and return to a pre–defined rendezvous point, where we crane it back onboard the ship.

"Adding to the problems are the sub zero water temperatures and the crushing pressures at 1000m depth. All systems on the vehicle must work perfectly while under the ice or it would be lost. There is no hope of rescue 60km in, with 500 metres of ice overhead."

The NOC describes Autosub's just-completed series of six cruises under the Pine Island shelf as "high risk" - understandably so. However, the yellow submarine carried out each mission without bother, bringing back large amounts of data for further analysis.

Boffins are particularly keen to figure out what's going on with the Western Antarctic ice shelves, as they have relatively little idea what sort of behaviour is normal. The Pine Island glacier has been getting thinner and moving into the sea faster since the 1970s, and the whole western shelf is currently putting enough loose ice into the ocean to raise sea levels by a quarter-millimetre annually.

"The picture we should get of the ocean beneath the glacier will be unprecedented in its extent and detail," says Adrian Jenkins of the British Antarctic Survey. "It should help us answer critical questions about the role played by the ocean in driving the ongoing thinning of the glacier."

Not least among the costs of the research will have been a substantial bill for batteries. The Autosub uses 5,000 alkaline D-cells on each trip, so the six-dive series will have seen 30,000 batteries used - some four tonnes of them. ®